First crowd-sourced book - The Talmud.

As scholars launch a crowd-sourced study of Madison's notes on the writing of the US Constitution, the parallel with the Talmud is plain.  For almost two thousand years in a dead language, religious scholars built a multilayer document.  Instead of clicking on links of links, you look in the margin of the margins for detail.

"Could we take a long, impenetrably-difficult text, and tease meaning out of it in a format that people could more easily approach? There is a model for this sort of thing, but it’s not a model from the American constitutional tradition; it’s the Talmud—the multi-volume exposition of Jewish law that developed after the Romans sacked the Temple in Jerusalem. The Talmud is a series of debates—and commentaries on those debates—on a text called the Mishnah. The rabbis found an ingenious way of commenting on this dry, lengthy text in a language (Ancient Hebrew) which was already in Roman times no longer their vernacular (they spoke and wrote in Aramaic). On a page of Talmud, a passage of Mishnah is physically surrounded by layers of commentary text, more and more of them as the centuries wore on. So in the center of the page is a short passage, by tradition, of course, Divine, but often in practice dry as dust; yet radiating out from that passage is centuries of wisdom and thought. It is not merely a form of crowd-sourced scholarship, but it is a visual means of expressing that scholarship and crowd-sourcing that seemed to me to have broad application to the exposition of lengthy and difficult historical texts like the Notes."